In Southcentral Alaska, salmon declines are pinned on a toothy invader

 

Earlier this month, I wrote about the Yukon River’s chinook salmon runs, which have lately plummeted for reasons that remain murky. While researchers are years from cracking that mystery, the Yukon isn’t the only Alaskan river losing its salmon. In the state’s Susitna River basin, which courses through Southcentral Alaska near Anchorage, the mighty fish has also crashed. And unlike in the Yukon, scientists may have pinpointed the culprit: Northern pike, a rapacious invader with an appetite for young salmon.

That pike are invasive in the Susitna is a curious artifact of Alaska’s rugged geography. The fish — snaky creatures whose long jaws are spiked with needle-like teeth — are native throughout the American Midwest and Canada, and they also naturally inhabit the entirety of northern Alaska. But the Alaska Range, a 400-mile-long band of mountains that curves from Lake Clark to the Canadian Yukon, historically blocked the pike from the state’s southern reaches.

In Southcentral Alaska, invasive Northern pike can grow to more than 30 pounds. Photo courtesy of the US Geological Survey.

That changed in the 1950’s. Scientists aren’t sure how pike ended up in southern Alaska, but the most likely explanation, says Adam Sepulveda, aquatic biologist with the U.S. Geological Survey, is that an ice-fishing aficionado airlifted them by floatplane.

Although it took a few decades for the pike population to grow large enough to harm salmon returns, the nosedive, when it came, was swift. In a Susitna tributary called Alexander Creek, for instance, the number of chinook escaping to their spawning grounds plunged from nearly 4,000 fish in 1999 to less than 200 in 2010. Anglers grew despondent; once-vibrant fishing camps were boarded up. "Pike are the only species where fishermen will buy me a beer when they find out I'm working on them,” Sepulveda says.


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